1. Field of the Invention
The present invention relates to a skeletal referenced method and instrument for establishing ligament graft tension and isometry, particularly during knee surgery involving the cruciate ligaments.
2. Description of the Prior Art
Although the present method and instrument have general application to proper orientation of a ligament graft between fixation sites on adjacent articulated bone structures, they have particular application to reconstructive surgery of the anterior and posterior cruciate ligaments of the knee, and especially isometric positioning of autogenous or prosthetic anterior cruciate ligament grafts.
In addition to proper graft selection, tensioning and fixation, correct isometric positioning of the anterior cruciate ligament graft is important to minimize postoperative complications such as stiffness and residual pathologic laxity.
By definition, "isometrically" positioned grafts maintain a constant length and tension throughout passive knee motion or flexion. Graft isometry is dependent on proper graft orientation. Malpositioning of the cruciate ligaments can result in limitation of knee motion or more likely, elongation of the graft as it experiences different tensions at different knee positions. Various graft orientations are commonly used clinically in the prior art and there is a need for an interoperative instrument to aid in locating the path for isometric graft placement by precisely establishing expected graft tension and displacement changes prior to graft fixation.
Skeletal referenced tensioning after the isometric path has been established is a particularly important need. Tensioning using extra skeletal means, as is routinely now done, is uncertain because when the graft is fastened to the selected site of fixation a transfer of load causes translation of force to movement in the connective bone structure, producing change in the distance between fixation sites and tension reduction in the graft.